Hot blooded? Scientists read dino body heat

Scientists at Caltech say they have measured the body temperatures of dinosaurs for the first time. As it turns out, we have a few things in common.

By analyzing the chemistry of dinosaur teeth, the researchers say they've discovered that giant, long-necked sauropods like those made famous in Jurassic Park had body temperatures in the same range as most mammals -- 96 to 100 degrees Fahrenheit.

"In a simple sense, they're warm," said John Eiler, geochemist and co-author of the freshly published finding. "They feel like us. If you went up and put a hand on their side, it would be like putting a hand on a cow."

The Jurassic beast named Brachiosaurus brancai, for example, similar to those pictured above, came in at 100.8 degrees.

The similar Camarasaurus would have given a reading of 96.3.

While researchers have suspected for years that many dinosaurs were "warm blooded," it's the first time measurements of fossils have yielded specific temperatures.

And there were a few surprises. The massive, plant-eating sauropods, for instance, were thought by many researchers to be "gigantothermic." They would stay warm, at least while alive, simply because they were so huge.

But the temperature readings based on teeth came in a few degrees cooler than the estimates for purely gigantothermic dinosaurs.

"Why were they colder?" Eiler asks. "Why did we mispredict the temperatures?"

The dinosaurs might have had some other mechanism for cooling down, such as air sacs in their bodies, but so far that's only a guess.

And we can't assume they were warm-blooded in the same was as mammals, Eiler said. Instead, the scientists' work could end up broadening ideas about metabolism, perhaps one day rendering the familiar cold-blooded, warm-blooded paradigm obsolete.

Eiler and the lead author of the study, post doctoral researcher Robert Eagle, looked at levels of rare isotopes, carbon 13 and oxygen 18, found in a mineral in 11 dinosaur teeth.

But they also analyzed how these isotopes -- versions of elements with differing numbers of neutrons -- were stuck together.

The bonding was the key to reading body temperature, Eiler said. Colder temperatures mean more bonding between rare isotopes; the warmer the temperatures, the less bonding.

The scientists laid the groundwork in a previous paper by making such measurements for the teeth of living animals, as well as woolly mammoths, which turned out to be indistinguishable from modern elephants.

After demonstrating that the technique worked, it was time to move on to dinosaurs.

Next on the list: smaller dinosaurs, including two-legged meat-eaters like the Velociraptors, also stars of Jurassic Park.

"This is like a beach head on the problem," Eiler said. "This will let us study in detail how metabolism and body temperature are related to each other in some of the most extraordinary creatures that ever walked the land."